The purpose of this study is to determine an adjuvant that will maximize antibody response and minimize animal pain and distress, thereby benefitting the experimental animal and improving the scientific result. Tissue reactions and antibody titers were compared using two common adjuvants, complete Freund's adjuvant and Ribi adjuvant, in rabbits. Results indicate that both adjuvants produce tissue reactions at the site of inoculation. Reactions caused by RIBI adjuvant were similar in nature but reduced in severity. It appears that RIBI adjuvant produces acceptable antibody titers when the antigen is a large protein (e.g., 700 kDa), but significantly lower levels than complete Freund's adjuvant when a small protein is used as antigen. These findings are consistent with recent reports (Deeb et al., Comparative antibody response and health effects using Ribi and Freund's adjuvants in rabbits, AALAS Abstract, 1991; Johnston et al., An evaluation of several adjuvant emulsion regimens for the production of polyclonal antisera in rabbits, AALAS Abstract, 1991). The next adjuvant that will be evaluated is Hunters TiterMax. Hunters TiterMax, a water in oil emulsion, is the newest adjuvant that has been marketed as an alternative to complete Freund's adjuvant. TiterMax contains no protein, bacterial or plant components, or Mycobacterium that would cause hypersensitivity reactions or granulomas. Rabbits will be clinically evaluated for pain and distress, and gross and histopathologic collections will be made. Antibody titers will also be evaluated and compared with complete Freund's adjuvant. These findings may help substantially in realizing the goal of an acceptable alternative to complete Freund's adjuvant.